Nano wires make tiny compasses

May 5/12, 2004

Researchers from the University of California
at Davis have built compass needles as small as 20 by 200 nanometers,
which is 3,000 times narrower than a human hair and 50 times narrower
than an E. coli bacterium.

The researchers' compass needles are just under half the size
of the previously smallest known compasses, which occur naturally in magnetotactic
bacteria that orient themselves using the earth's geomagnetic field.

The researchers' nanocompass could be used to measure magnetic
fields at the nanoscale and to orient nanosized wires during the process
of building molecular-sized structures; they could also be used to magnetically
steer or manipulate nanostructures suspended in solution, according to
the researchers.

The researchers made the device by stringing particles of magnetite,
or iron oxide, on nanowires made from lithium molybdenum selenide. Each
magnetite particle is as small as seven nanometers in diameter, which
is seven times smaller than those found in magnetotactic bacteria. The
researchers' needles are superparamagnetic at room temperature, meaning
they measure stronger magnetic fields than the bacteria's compasses, which
are sensitive to the earth's extremely weak magnetic field.

The researchers are working on improving the assembly and purification
of their minuscule compass needles to make them consistent enough for
commercial applications.

It will be two to five years before the magnetic compass can be
used in advanced devices, according to the researchers.

The work was presented on April 1, 2004 at the American Chemical
Society (ACS) national meeting in Anaheim, California.